Weather Words: Landslide

A landslide is a sudden and powerful movement of rock, soil, and debris down a slope. They happen when the forces pulling materials downhill—mainly gravity—overcome the strength holding them in place. Landslides can vary in size from small slumps that move just a few feet to massive slides that reshape entire hillsides in seconds. While steep terrain is naturally more vulnerable, landslides can occur almost anywhere that slopes, soil, and water interact in the wrong combination.

One of the biggest triggers for landslides is heavy rain. When the ground becomes saturated, water fills the spaces between soil particles, reducing friction and weakening the slope’s stability. Once that balance tips, gravity takes over and the hillside begins to move. This is why landslides are especially common after long periods of rainfall or during and after tropical systems, like hurricanes or tropical storms, that can dump several inches of rain in just a few hours.

But rain isn’t the only factor. Earthquakes, volcanic activity, wildfires that strip away vegetation, and even human construction can all set the stage for a slide. The results can be devastating: destroying homes, blocking roads, and altering rivers and landscapes. Understanding landslides helps scientists and emergency managers issue warnings and help protect people who might be in harm's way from potential landslides.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.